This application relates generally to photography and, more particularly, to a multicolor diffusion transfer photographic system.
Diffusion transfer photographic systems wherein images are formed in color by the use of dye developers are well known in the art. Generally, multicolor transfer images are formed by processing an exposed multicolor photosensitive silver halide element with a processing composition distributed between two sheet-like elements, one of the elements including an image receiving layer. The processing composition is so applied and confined within and between the two sheet-like elements as not to contact or wet outer surfaces of the two superposed elements, thus providing a film unit whose external surfaces are dry. The processing composition, which may be viscous or non-viscous, preferably is distributed in viscous form from a pressure rupturable container. Such pressure-rupturable processing composition containers are commonly referred to as "pods".
Multicolor diffusion transfer images may be obtained using dye developers by several techniques. A particularly useful technique employs an integral multilayer photosensitive element such as is disclosed in U.S. Pat. No. 2,893,606 and in U.S. Pat. No. 3,345,163 wherein at least two selectively sensitized photosensitive strata, superposed on a common support, are processed, simultaneously and without separation, with a single (common) image-receiving layer. A suitable arrangement of this type for obtaining multicolor images utilizing subtractive color principles comprises a support carrying a red-sensitive silver halide emulsion stratum, a green-sensitive silver halide emulsion stratum and a blue-sensitive silver halide emulsion stratum, said emulsions having associated therewith, respectively, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be positioned in the silver halide emulsion stratum, for example in the form of particles, or it may be disposed in a stratum behind the appropriate silver halide emulsion stratum with respect to the exposing light. Each set of silver halide emulsion and associated dye developer strata may be separated from other sets by suitable interlayers, for example, by a layer or stratum of gelatin, polyvinyl alcohol, or other polymeric materials known in the art. In certain instances, it may be desirable to incorporate a yellow filter in front of the green-sensitive emulsion to avoid improper exposure of said emulsion, by blue light, and such a yellow filter may be incorporated in the appropriately positioned interlayer. However, such a separate yellow filter may be omitted where a yellow dye developer of the appropriate spectral characteristics is present in a quantity and state capable of functioning as the requisite yellow filter. Procedures and suitable components for preparing such integral multicolor photosensitive elements are described in numerous patents and are well known in the art.
Following photoexposure, the photosensitive element is processed by application of a processing composition, for example, by immersion, coating, spraying, flowing, etc., in the dark. The exposed photosensitive element may be superposed prior to, during, or after application of the processing composition on a sheet-like element which may include an image-receiving layer. In one commercial embodiment, the processing composition is applied to the photosensitive element in a substantially uniform layer as the photosensitive element is brought into superposed relationship with the image-receiving layer. The liquid processing composition permeates the layers of the photosensitive element to initiate and effect development of the latent images contained therein. The dye developers are immobilized or precipitated imagewise in developed areas as a consequence of and in proportion to the silver halide development. This immobilization is, at least in part, due to a change in the solubility characteristics of the dye developers upon oxidation and especially as regards its solubility in alkaline solution. In undeveloped and partially developed areas of the silver halide emulsion layers, the respective unoxidized (unreacted) dye developers are diffusible. Development thus provides an imagewise distribution of unoxidized dye developer, diffusible in the alkaline processing composition, as a function of the point-to-point degree of exposure of a silver halide emulsion layer. At least part of each of these imagewise distributions of unoxidized dye developer is transferred by imbibition to a superposed image-receiving layer, said transfer substantially excluding oxidized dye developer. The image-receiving layer receives a depthwise diffusion, from each developed silver halide emulsion, of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide a reversed or positive color image of each developed silver image. The image-receiving layer may contain a mordant and/or other agent to immobilize the dye developer transferred thereto. If the color of a transferred dye developer is affected by changes in the pH of the image-receiving layer, this pH may be adjusted in accordance with well known techniques to provide a pH affording the desired color. In the preferred embodiments of U.S. Pat. No. 2,983,606 and in certain commercial applications thereof, the desired positive multicolor image is viewed by separating the image-receiving layer from the photosensitive element at the end of a suitable imbibition period.
In another commercial application of the dye developer process the image-receiving layer is not separated from its superposed relationship with the photosensitive layers subsequent to formation of the transfer image. Instead the color image is viewed through a transparent support. The '606 patent discloses such an embodiment wherein the processing composition includes a white pigment, such as titanium dioxide, in an amount effective to mask or "hide" from view the developed silver halide emulsions now positioned behind the image-receiving layer when the image-receiving layer is viewed through the transparent support.
U.S. Pat. No. 3,415,644 discloses and claims photographic products and processes wherein a photosensitive element and an image-receiving element are maintained in fixed, superposed relationship prior to exposure and this relationship is maintained as a laminate after processing and transfer image formation. The multicolor transfer image is viewed through a transparent (support) sheet against a reflecting, i.e., white, background. Photoexposure is made through said transparent support and the layers carried thereon, including the image-receiving layer, and application of the processing composition provides a layer of light-reflecting material to provide a white background. The light-reflecting material (referred to in said patent as an "opacifying agent") is preferably titanium dioxide but a number of other materials have been disclosed as useful. In addition to providing a masking layer so the transfer image may be viewed without interference by the images in the developed silver halide emulsions, the light-reflecting material also performs an opacifying function by reflecting ambient light passing through the image-receiving layer and its transparent support when the photoexposed film unit is removed from the camera before transfer image formation is completed, thereby acting to protect the photoexposed silver halide emulsions from post-exposure fogging by such light.
U.S. Pat. No. 3,647,437 is concerned with improvements in the above-mentioned processes, and discloses the provision of a light-absorbing material, sometimes referred to as an optical filter agent, to permit such processes to be performed outside of the camera in which photoexposure is effected and to be so performed under much more intense ambient light conditions. The light-absorbing material or optical filter agent, preferably a dye, is so positioned in the film unit and/or constituted as not to interfere with photoexposure (by absorbing light during photoexposure) but so positioned between the photoexposed silver halide emulsions and the transparent support during processing after photoexposure as to absorb light which otherwise might fog the photoexposed emulsions. Furthermore, the light-absorbing material is so constituted and/or positioned after processing as not to interfere with viewing the desired image in its proper colors shortly after said image has been formed. In the preferred embodiments, the optical filter agent is a dye and is initially contained in the processing composition together with a light-reflecting material, e.g., titanium dioxide. The concentration of this light-absorbing dye is selected to provide the light transmission opacity required to perform the particular process under the selected light conditions, and a plurality of such dyes selected to together provide absorption over the visible spectrum is utilized in multicolor embodiments.
In a particularly useful embodiment, the light-absorbing dye is highly colored at the pH of the processing composition, e.g., 13-14, but is substantially non-absorbing of visible light at a lower pH, e.g., less than 10-12. This pH reduction may be effected by an acid-reacting reagent appropriately positioned in the film unit, e.g., in a layer between the transparent support and the image-receiving layer. Suitable acid-reacting reagents, preferably polymeric acids, are disclosed in the '644 and '437 patents.
Suitable materials for use as image-receiving layers are disclosed in the aforementioned patents. The image-receiving layers may comprise polyvinyl alcohol or gelatin containing a dye mordant such as poly-4-vinylpyridine as is disclosed in U.S. Pat. No. 3,148,061.
As disclosed in the previously cited patents, the liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example, sodium hydroxide, potassium hydroxide, and the like, and preferably possesses a pH in excess of 12, and most preferably includes a viscosity-increasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. Preferred film-forming materials comprise high molecular weight polymers such as polymeric, water-soluble ethers, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose, which are substantially inert in alkaline solution. Other film-forming materials or thickening agents whose ability to increase viscosity is unimpaired if left in alkaline solution for extended periods of time also may be used. The film-forming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity appropriate for the particular method of application to be used, such viscosity being in excess of 100 cps, at a temperature of approximately 24.degree. C. and preferably in the order of 100,000 cps. to 200,000 cps. at that temperature.
Dye developers are well known in the art and are compounds which contain both a silver halide developing function and the chromophoric system of a dye. By "a silver halide developing function" is meant a grouping adapted to develop exposed silver halide. The dye developer as incorporated in the photosensitive element may have a "latent" silver halide developing function, i.e., the dye developer may contain a moiety which is a precursor of the silver halide developing function or moiety, the active functional group being formed in situ following application of the processing composition, e.g., by alkaline hydrolysis of an esterified hydroquinonyl group. A preferred silver halide developing function is a hydroquinonyl group. Other particularly useful developing functions include orthodihydroxyphenyl and ortho- and para-amino substituted hydroxyphenyl groups. In general, the developing function includes a benzenoid silver halide developing function, that is, an aromatic silver halide developing group which forms quinonoid or quinone substances when oxidized. The dye developers usually are selected for their ability to provide colors useful in carrying out subtractive color photography, e.g., cyan, magenta and yellow. Other colors, of course, may be provided to meet the needs of a particular system.
In such multicolor applications of diffusion transfer color processes, variations in manufacturing conditions may result in undesirable variations in the sensitometric response, e.g., speed or contrast, of one silver halide emulsion relative to that of either or both of the other silver halide emulsions. Such undesirable variations may be reflected in changes of the H and D curve of, for example, the red record relative to the H and D curves of the green and blue records and may be manifested in the ultimate multicolor image as a shift in color balance, for example, toward the red.
U.S. Pat. No. 3,899,331 discloses a technique for reducing or avoiding such effects by performing the process in the presence of pyrazolo (3,4-d) pyrimidine compounds. The present application relates to the use of cyclic ligands in diffusion transfer photographic products and processes to improve the sensitometric response of a multicolor photosensitive element.